ARM: LPC32xx: Cleanup USB clock init

Move most of usb clock initialization from lpc32xx_udc and ohci-nxp to
clock.c. Also adds ohci clocks and otg clocks.

Signed-off-by: Alexandre Pereira da Silva <aletes.xgr@gmail.com>
Signed-off-by: Roland Stigge <stigge@antcom.de>